CRUSTACEA. 



497 



the natatory feet are delicate chitinous lamellae, in the spaces 

 between which the cirriform feet of the adult become developed. 

 The ventral spinous process of the Nauplius stage is much reduced, 

 though usually three-jointed. It becomes completely aborted 

 after the larva is fixed. 



In addition to the antennary gland there is present, near the 

 dorsal side of the body above the natatory feet, a peculiar paired 

 glandular mass, the origin of which has not been clearly made 

 out, but which is perhaps equivalent to the entomostracan shell 

 gland. It probably supplies the material for the shell in suc- 

 ceeding stages 1 . 



The free Cypris stage is not of long duration ; and during it 

 the larva does not take food. It is succeeded by a stage known 

 as the pupa stage (fig. 232 B), in which the larva becomes fixed, 

 while underneath the larval skin the adult structures are de- 

 veloped. This stage fully deserves its name, since it is a quies- 

 cent stage during which no nutriment is taken. The attachment 

 takes place by the sucker of the antennae, and the cement gland 

 (/) supplies the cementing material for effecting it. A retro- 

 gressive metamorphosis of a large number of the organs sets in, 

 while at the same time the for- 

 mation of new adult structures 

 is proceeded with. The eyes 

 become gradually lost, but the 

 Nauplius eye is retained, though 

 in a rudimentary state, and the 

 terminal joints of the antennae 

 with their olfactory hairs are 

 thrown off. The bivalve shell 

 is moulted about the same time 

 as the eyes, the skin below it 

 remaining as the mantle. The 

 caudal process becomes abor- 

 ted. Underneath the natatory 



FIG. 232. LARVAL FORMS. OF THE 

 THORACICA. (From Huxley.) 



A. Nauplius of Balanus balanoides. 

 (After Sp. Bate.) B. Pupa stage of Lepas 

 australis. (After Darwin.) 



n. antennary apodemes; /. cement 

 gland with duct to antenna. 



1 There is considerable confusion about the shell gland and antennary gland. In 

 my account Willemoes Suhm has been followed. Glaus however regards what I have 

 called the antennary gland as the shell gland, and states that it does not open into the 

 antennas till a later period. He does not clearly describe its opening, nor the organ 

 which I have called the shell gland. 



B. II. 32 



